Premium
Kinetics of the reactivation of the Hill reaction in CO 2 ‐depleted chloroplasts by addition of bicarbonate in the absence and in the presence of herbicides
Author(s) -
Snel Jan E. H.,
Rensen Jack J. S.
Publication year - 1983
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1983.tb02763.x
Subject(s) - bicarbonate , chemistry , dcmu , hill reaction , kinetics , thylakoid , sodium bicarbonate , photosynthesis , medicinal chemistry , photosystem ii , biochemistry , chloroplast , organic chemistry , quantum mechanics , gene , physics
In isolated broken chloroplasts photosynthetic electron transport requires the presence of CO 2 and/or bicarbonate. This bicarbonate effect on electron flow was measured in a medium containing 100 m M sodium formate. In this medium a dark incubation time with bicarbonate is required for the reactivation of the Hill reaction. We have measured the kinetics of the reactivation of electron flow by varying the dark incubation of CO 2 ‐depIeted pea ( Pisum sativum L., cv. Rondo) chloroplasts with bicarbonate. The half‐time of this reactivation appears to be 25 s when 2 m M bicarbonate is added. The dinitrophenol herbicide, i ‐dinoseb, is shown to be a competitive inhibitor of the bicarbonate dependent Hill reaction with an inhibitor constant (K i ) of 31 n M . In the presence of 100 n M i‐dinoseb or 100 n M DCMU the half‐time of the reactivation by 2 m M bicarbonate appears to increase to about 58 s. We provide an explanation for these phenomena by analyzing the bicarbonate‐thylakoid interaction on the basis of a simple reaction scheme. The binding of bicarbonate to the thylakoids appears to be a second order reaction with pseudo‐first order kinetics. According to our analysis, any inhibitor, which is competitive with respect to the bicarbonate stimulation of the Hill reaction, should increase the half‐time of the reactivation of the Hill reaction.